Molucca’s thousand-odd islands (one count claims 999; another 1029) estend across an area of some 851000 square kilometers, only 10 percent of which is land. Geologically, biologically and culturally, these islands form a fascinating zone of transition between the Sunda Islands to the west and the Sahul zone in the east.
In geological terms, the Molucca island chain is an infant, no more than a few million years old. Still, it is amazingly complex. Three of the earth’s great tectonic plates meet in the Moluccas. The plate collide directly, scrape past each other, force another plate up or down, or fragment, producing a variety of geological effects. The result is the great, 6000-kilometer-long Indonesian Ring of Fire. One end is marked by the Nicobar and Andaman islands; the other, the arc leading up through Molucca and into the Philippines.
Though Molucca, this island arc is split. In the south, the outer arc is formed of contorted, mostly calcareous mudstones, limestones, and a some rare intrusive rock. This outer arc marks the northern boundary of the shallow Arafura Sea. It begins in the west with the barren, uplifted coral reefs of the Leti and Babar islands, and continuing counterclockwise, includes the forested, slightly larger Tanimbars, the Kei, Watubela and Gorong groups, and finally hooks sharply back to include large, almost inaccessibly mountainous, Seram and Buru. Somewhat east of this outer arc is the Aru group, built a raised coral reefs cut through with narrow, mangrove-lined channels.
The inner arc is geologically quite different. A continuation of a chain that includes Sumatra, Java and Bali, here are the volcanic islands, beginning with large Wetar in the west, and extending northeast through the Damar group to include tiny Fire Mountain in Banda. These islands mark a plate boundary, where molten rock has worked up through fissures in the earth’s crust.
North of Seram, the double line of islands becomes less clear. The strangely shaped island of Halmahera (like Sulawesi, formed by the slow collision of two narrow islands) is marked on its western side by a line of young, active volcanoes, including Ternate. The rest of Halmahera is made up of older volcanic rock, calcareous sediments, and ultrabasic materials forced up from beneath the ocean.
Taliabu and Mangole Islands are anomalous, having been formed when granitic fragments of the earth’s crust were torn from the land mass of New Guinea and carried several hundred kilometers away by currents of magma. These islands disrupt the symmetry of the double chain.
(PeriPlus)